Were you focused on just making it work on the iPhone, or do you think you will keep adding functionalities to the app? Do you think it will ever be possible to train one's own model on an iPhone?
I think that fine-tuning the whole model (a.k.a. Dreambooth) on iPhone would require more RAM / processing power than it currently has. More viable path is to implement Hypernetwork + Textual Inversion, that is within possibility of today's hardware.
(Note that at that time, there is an implemention bug in inpainting model that caused the weirdness that I need to manually fix)